The field of present invention is that of the operating turbomachines such as hydraulic turbopumps, axial compressors, and radial or radial-axial compressors, driven by electric motors, and relates in particular to the structure of the casing of such a machine.
There are known casings of universal electric motors, i.e. motors which can be coupled to any user device or operating machine. In particular, a motor casing with forced air ventilation is known and described in Italian patent application No. 85621/A/88 filed on 8.26.1988, and assumed included herein by reference by way of example, with regard to the structure of the jacket. In such known motor casing, a pair of cylindrical jackets are arranged coaxially so as to form a toroidal interspace which is open at the end sections thereof and divided by ribs to define longitudinal channels for the cooling air impelled by a fan fitted on the motor shaft. In this casing, at the end thereof adjacent to the cooling fan there is arranged a first flange which supports with a central portion thereof a first rotor bearing. The other end the casing is closed by a second flange which supports a second rotor bearing and is connected with a universal coupling flange suitable for coupling with any standard operating machine. Such two end flanges therefore essentially have the function of supporting the bearings of the motor shaft and only one of them also has a coupling function.
As is known, if the machine is a fluid impelling machine, the coupling structure of the casing must also provide, amongst others, a sealing function against the fluid to be processed.
In another known motor casing structure, which is specifically intended for coupling with a hydraulic pump, the coupling assembly essentially includes at least three flanges, the first of which supports a rotor bearing and simultaneously provides a fixing point for the outer body of the pump. A second flange, or sealing shield, provides a seal against the fluid to be processed and defines at the same time the closure wall of the pump diffuser a third flange, essentially frustoconically shaped, stiffens and connects the first two flanges. Though this known structure entails some advantages with respect to the prior art, it is not free from disadvantages, among which mention is made, first of all, of the fact that the sealing rings mounted on the second flange are subjected to axial movements with respect to those mounted on the motor shaft, consequently causing a considerable loss of efficiency of the seal and occasional leakage of fluid. This is caused by the fact that the second flange is forced by the internal pressure of the impelled fluid, and "breaths" like a sort of plenum chamber independently from the first flange supporting the bearing, and therefore the central region of the second flange carrying the sealing ring is subjected to axial movements which are generally opposite to the axial displacemants of the motor shaft due to the fluidodynamic reaction exerted on the impeller.
A further disadvantage resides in the substantial considerable complexity of construction the assembly, which is formed by a large number of components and furthermore requires numerous and rather laborious welds, with obviously nagative effects on both the quality and the final precision of the assembly as well as on production costs.